Process for chemical vapor deposition of zirconium carbide

ABSTRACT

Deposition of zirconium carbide on a substrate is advantageously effected by reacting zirconium and methyl iodide under heating. The deposition of zirconium carbide is useful for coating of a rocket nozzle surface, coating of granular fuels for gas cooled nuclear reactor and the like.

United States Patent [191 Ikawa et al.

[ Apr. 16, 1974 PROCESS FOR CHEMICAL VAPOR DEPOSITION OF ZIRCONIUM CARBIDE Inventors: Katsuichi Ikawa; Fumiaki Kobayashi; Kazumi Iwamoto, all of Ibaragi, Japan Japan Atomic Energy Research Institute, Tokyo, Japan Filed: Sept. 20, 1971 Appl. No.: 181,753

Assignee:

Foreign Application Priority Data [56] References Cited UNITED STATES PATENTS 3,619,129 11/1971 Chiola 423/492 3,399,980 9/1968 Bourdeau 3,459,504 8/1969 Bracken et a1 117/106 Primary Examiner-Alfred L. Leavitt Assistant ExaminerJ. Massie Attorney, Agent, or Firm-Stevens, Davis, Miller & Mosher [5 7] ABSTRACT Deposition of zirconium carbide on a substrate is advantageously effected by reacting zirconium and methyl iodide under heating. The deposition of zirconium carbide is useful for coating of a rocket nozzle surface, coating of granular fuels for gas cooled nuclear reactor and the like.

8 Claims, 2 Drawing Figures PROCESS FOR CHEMICAL VAPOR DEPOSITION OF ZIRCONIUM CARBIDE BACKGROUND OF THE INVENTION 1. Field of the Inv eiTtion The present invention relates to process for chemical vapor deposition of zirconium carbide and is characterized by the use of methyl iodide and metallic zirconium as starting materials.

Z Description of the Prior Art M Practical application of the chemical vapor deposition of zirconium carbide is expected in the industrial fields such as coating of the surface of rocket nozzle which is exposed to jet gas, coating of granular fuels of gas cooled high temperature nuclear reactor and the like. However, the technical levels at the moment are insufficient to perform practical applications and accordingly thisindustrial field has not yet been established. Therefore, the experiments which have been tried hitherto are explained herein-below.

In the chemical vapor plating process which has been tried hitherto, zirconium tetrachloride and hydrocarbons are used as starting materials and free zirconium and carbon are simultaneously deposited on the surface of the substrate by pyrolyzing these starting materials in hydrogen atmosphere. However, this process has not only the defect of danger from the use of hydrogen gas, but also the following essential defects in the operation. That is, zirconium tetrachloride is commercially available only in powdered form and consequently it is difficult to control the evaporation rate of this material. Therefore, it is difficult to keep constant the ratio of the supplying rates of zirconium tetrachloride and hydrocarbon to the deposition zone during operation.

Recently, the use of metallic zirconium and chlorine gas as the starting materials instead of zirconium tetrachloride was tried and these materials were allowed to react in a reaction zone which is followed by a deposition zone, in order to generate continuously vapor of zirconium tetrachloride near the deposition zone. But, in this case, the supplying rates of the two starting materials (chlorine gas and hydrocarbon) should be controlled simultaneously and, furthermore, the use of chlorine gas results in additional troublesome problems on the selection of the material for the gas inlet piping system and on health and the like.

In the present invention, neither zirconium tetrachloride, hydrogen gas nor chlorine gas is used, and the object of the invention is to eliminate the defects in the above processes which have been proposed, by the use of methyl iodide and metallic zirconium as starting materials.

SUMMARY OF THE INVENTION.

The present invention relates to a process for chemical vapor deposition of zirconium carbide in which methyl iodide and metallic zirconium are used as starting materials.

Theprocess for chemical vapor deposition of zirconium carbide according to the present invention preferably comprises the steps of pyrolyzing methyl iodide and simultaneously reacting the pyrolized product with metallic zirconium in the reaction zone heated at about 600-850C, preferably at 700-800C, the mixture of the reaction products then being supplied to the deposition zone heated above 900C, preferably at 900 1 ,400C, the deposition zone being connected to the? end of the reaction zone. In this process, a large excess of metallic zirconium is charged in the reaction zone about 600800C. Moreover, the iodine reacts with metallic zirconium abovef00 Cfandre sultsfifheTfi mation of zirconium tetraiodide which liberates metallic zirconium more easily than zirconium tetrachloride used in other processes previously mentioned. On the other hand, methyl radicals associates in a moment to form ethane. The role of the ethane in this process has an effect similar to that of the hydrocarbon in other process previously mentioned.

By controlling the temperature distribution from the reaction zone to the deposition zone, the effective mole ratio of ethane to zirconium iodide can be obtained, to form desirable deposition layer without liberating carbon from the ethane before the deposition zone. Accordingly, the atomic ratio of carbon to zirconium in the deposition layer can be easily controlled so as to keep the stoichiometry of the zirconium carbide.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a schematic diagram of a preferred apparatus for the application of the present invention.

FIG. 2 shows the X-ray diffraction patterns of the vapor deposited material resulting from the application of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Now, the invention is illustrated by way of working example. The example is given for better understanding of the present invention and should not be taken as limiting the scope of the invention. It is to be understood that any change and modification within the spirit and scope of this invention can be effected.

EXAMPLE FIG. 1 shows the schematic diagram of an apparatus with which the example of the present invention was carried out. An arrow shows the direction of gas stream. The heating zone comprises two cylindrical electric furnaces which are closely jointed to each other; that is, 16 mm ID. alumina tube is inserted into a nichrome resistance furnace 1 and a platinum resistance furnace 2, and the former is for reaction zone and the latter is for deposition zone. When the temperature of nichrome resistance furnace 1 was set at 800C and that of the platinum resistance furnace 2 was at 1,400C respectively, the temperatures of the inner wall of the furnace tube were 740C at maximum in reaction zone and l,300C at maximum in deposition zone. Thus, for both heating zones, gently-sloping temperature gradients were given over the whole length of each furnace. Zirconium sponges 4, 5 10 mm in diameter, were charged in the reaction zone over almost its whole length, and two small alumina plates 5 and 6 as substrates for deposition were positioned where the temperatures showed 1,050C and l,2l0C respectively in the deposition zone.

Then, vapor of methyl iodide which was vaporized in a vaporizer, not shown, cooled at C, was supplied to the reaction zone by the stream of argon gas with the flow rate of 120 cm per minute. The gas stream from the outlet of the furnace tube 3 was exhausted through an oil bubbler 8. After 1 hour, the supply of the vapor of methyl iodide was stopped, and 20 minutes thereafter the electric current to the furnaces was cut off. When the temperature of platinum resistance furnace 2 fell to 400C, the small alumina plates 5 and 6 mentioned above were taken out of the furnace into the atmosphere. Gray deposits were observed on these plates. These deposits were investigated by means of X-ray diffraction technique.

FIG. 2 shows X-ray diffraction patterns for the deposits which were obtained by the process in the above example. The upper pattern is for the deposit on the plate 5 which was heated at 1,050C, and the lower is for the deposit on the plate 6 at 1,210C, and both patterns show that these deposits are of zirconium carbide.

[n the above example, small alumina plates were used as substrates for deposition. However, any conventional substrates made of other materials can be used according to the purpose. In other words, the composition and the shape of substrate is not restricted if its material does not react strongly with zirconium carbide at deposition temperature.

What is claimed is:

l. A process for chemical vapor deposition of zirconium carbide on a substrate, which comprises reacting zirconium and methyl iodide in a reaction zone under heating;

supplying the reaction product to a deposition zone heated above about 900C; and then effecting deposition of zirconium carbide on a substrate placed in the deposition zone.

2. A process of claim 1, which comprises pyrolyzing methyl iodide, reacting the resulting iodine with zirconium; and subjecting the mixture of reaction products to pyrolysis and deposition on a substrate.

3. A process of claim 1, in which an inert gas is employed as carrier gas.

4. A process of claim 3, in which the inert gas is argon.

5. The process of claim 1, in which the deposition is carried out by using an apparatus comprising a reaction zone and a deposition zone connected to the reaction zone, said reaction being effected in the reaction zone and said deposition being effected in the deposition zone.

6. A process of claim 5, in which the apparatus is op- 551a at abou t 6017 851??? forfhifieatfin z tm e and at about 900-l400C for the deposition zone.

7. The process of claim 5, in which the apparatus is operated at about 700-800C for the reaction zone.

8. The process of claim 1, in which zirconium sponge is employed as said zirconium. 

2. A process of claim 1, which comprises pyrolyzing methyl iodide, reacting the resulting iodine with zirconium; and subjecting the mixture of reaction products to pyrolysis and deposition on a substrate.
 3. A process of claim 1, in which an inert gas is employed as carrier gas.
 4. A process of claim 3, in which the inert gas is argon.
 5. The process of claim 1, in which the deposition is carried out by using an apparatus comprising a reaction zone and a deposition zone connected to the reaction zone, said reaction being effected in the reaction zone and said deposition being effected in the deposition zone.
 6. A process of claim 5, in which the apparatus is operated at about 600* - 850*C for the reaction zone and at about 900* -1400*C for the deposition zone.
 7. The process of claim 5, in which the apparatus is operated at about 700*-800*C for the reaction zone.
 8. The process of claim 1, in which zirconium sponge is employed as said zirconium. 